Critical caveat: Memantine has a 60-80 hour half-life and steady-state takes ~2 weeks. Most subjective effects (good and bad) only manifest fully after this load-up window. Single-dose experiments don't tell you what 5 mg/day for 4 weeks feels like.

Onset on first dose (5 mg): 2-3 hours to peak plasma. Most users report nothing detectable from a single 5-10 mg dose. A subset (maybe 30%) report mild brightening of color perception, slight head-pressure, mild tingling — usually attributable to expectancy or to the early NMDA-block-from-zero effect.

Steady-state at 5-10 mg/day (biohacker dose, week 2-4):

• Subtle anxiolytic baseline shift. Most consistently reported. Users describe "less reactive," "less neuroticism," "less rumination," "edges off." Comparable in flavor to low-dose buspirone or theanine. Not sedating. Not euphoric.
• Subtle cognitive flatness in some users. A minority (~20-30% of forum reports) describe word-finding hesitation, slight short-term memory wobble, slight emotional muting in the first 2-4 weeks; reports indicate this often resolves by week 6 of continuous use.
• Stimulant feel "stays fresh" in users co-administering caffeine, modafinil, or amphetamines. Hardest to verify subjectively because the effect would be the absence of expected tolerance. Anecdote-grade.
• No characteristic "high" or "boost" — memantine is not a felt-effect compound. Most users titrating from 5→10→15→20 mg over 4 weeks (the Alzheimer's titration) report nothing dramatic until they hit 15-20 mg, where dissociative-tier effects start appearing in some users.

At 15-20 mg/day (clinical Alzheimer's dose):

• Dissociation-flavored effects in a subset. "Slight unreality," "distance," "looking through the world." Comparable to low-dose DXM or sub-anesthetic ketamine in flavor. PsychonautWiki classifies memantine as a dissociative at 12+ mg.
• Cognitive blunting more reliable than at 10 mg. Word-finding hesitation, slight executive slowness. Variable — some users feel sharp at 20 mg, others feel slow.
• Mild dizziness, especially on standing. Common. Resolves with hydration.

At 30+ mg/day (off-label / recreational):

• Full dissociative experience. Memantine has a small but real recreational use base — not popular because the long half-life makes recreation unwieldy (you don't recover in a day; you accumulate over a week). PsychonautWiki and forum reports describe "manic-like elevation" and "dissociative immersion" at high single doses, with persistent cognitive effects for days.

Variability: High. ~30% no detectable effect at 5 mg, ~30% strong subjective brightening or anxiolysis at 5 mg, ~20% paradoxical cognitive blunting that requires titrating slowly. Individual NMDA-receptor genetic variation (NR1I2 rs1523130, GRIN2A/B variants) plausibly drives some of this but is not characterized.

Comparison to other NMDA-acting compounds in Dylan's V5:

• Heavier than agmatine (which is a modest GluN2B-preferring antagonist with no felt effect) but much lighter than ketamine (which is a high-affinity blocker with strong dissociation at therapeutic doses).
• Different from magnesium (Mg²⁺ is the physiological voltage-block; memantine is a kinetically distinct add-on).
• Not comparable to NAC (NAC is glutathione precursor + cystine-glutamate antiporter; different mechanism).

• Tolerance buildup: Minimal-to-none for the NMDA antagonism. The pharmacology doesn't show classical receptor downregulation with chronic use; if anything chronic memantine reduces NMDA receptor surface expression in some preparations (which would be the "tolerance" but is also the therapeutic mechanism in AD). Subjective "wears off" reports from biohackers usually reflect the loss of the early novelty/dissociation response, not pharmacological tolerance.

• Recommended cycle: None required. Memantine is designed for chronic daily use; the long half-life means you're effectively on it for a week even after stopping. Cycling on/off short-term doesn't make pharmacological sense given the half-life.

• Reset protocol if needed: Discontinue and wait 2 weeks for full washout (4× half-life ≈ 12 days). Re-titrate from 5 mg if restarting. No withdrawal syndrome on sudden discontinuation, but very mild rebound dizziness/agitation has been reported anecdotally.

Synergistic with

• modafinil: The whole biohacker rationale. Theoretical: modafinil DAT-inhibition produces some downstream NMDA-mediated neuroadaptation; memantine intercepts the tolerance-side of that. Practical: modafinil tolerance is already minimal at Dylan's dose (100 mg 5-6×/week), so the synergy is mostly hypothetical. No interaction risk — modafinil is metabolized by CYP3A4/2C19, memantine bypasses CYPs entirely.

• cerebrolysin: Strong theoretical synergy in TBI / post-concussion / cognitive aging. Cerebrolysin is a neurotrophic peptide cocktail that promotes survival/repair pathways; memantine prevents excitotoxicity-driven death. Mechanism-complementary, not redundant. No documented interactions. If Dylan deploys memantine post-concussion, cerebrolysin is the natural co-administration.

• magnesium (especially L-threonate, already in V4): Mg²⁺ is the upstream physiological NMDA voltage-block; memantine takes over when depolarization expels Mg²⁺ during pathological signaling. Two complementary lines of defense against excitotoxicity. Excellent stack-safety. The Magtein in Dylan's V4 is a pre-deployed substrate for memantine if/when memantine is added.

• NAC (already in V4): NAC operates upstream via the cystine-glutamate antiporter (system Xc⁻) and via glutathione synthesis. Memantine operates at the receptor. Different layers of glutamate/excitotoxicity defense. No interaction concerns.

• Methylphenidate / amphetamines (Biederman ADHD adjunct evidence): Documented B-tier benefit on executive function deficits when memantine added to OROS-MPH or dextroamphetamine in adult ADHD. Mechanism: glutamate-dopamine cross-talk in PFC. Not relevant for Dylan's planned V5 (no classical stimulants planned).

• L-theanine (already in V4): Mild theoretical NMDA-modulation overlap (theanine is a weak NMDA modulator + glutamate-receptor binder). Combination is well-tolerated; no documented adverse interactions. Both contribute mild anxiolytic baseline.

• Donepezil / cholinesterase inhibitors: Standard-of-care combination in moderate-severe Alzheimer's (Tariot 2004; multiple subsequent confirmations). Not relevant for Dylan but demonstrates excellent in-human stack-safety.

Avoid stacking with

• Other NMDA antagonists (ketamine, dextromethorphan, amantadine, phencyclidine, MK-801): Compounded NMDA blockade — theoretical risk of dissociation, neuropsychiatric AEs, possible Olney's-lesion-like neurotoxicity at high combined exposures. EMA product information explicitly warns against amantadine and dextromethorphan co-administration. The 2021 JADER Japanese pharmacovigilance database analysis (Sato et al.) found mostly reassuring real-world safety with these combinations, but the conservative position holds for Dylan: don't stack memantine with other NMDA antagonists without medical supervision. Practical implication: if Dylan ever does ketamine therapy, memantine should be discontinued well in advance (>2 weeks for washout).

• agmatine (V5 candidate, already on Dylan's radar): Agmatine is a modest GluN2B-preferring NMDA antagonist. Combined with memantine = compounded NMDA blockade. Not a hard contraindication — agmatine's NMDA contribution at oral doses is much weaker than memantine's, so the practical risk is low — but the combination is uncharacterized in humans. Recommended approach: if Dylan deploys both, start each one alone first (4-6 week trial), then introduce the other while observing for additive cognitive blunting or dissociation. The agmatine compound file already flags this.

• neboglamine: Theoretical opposite-direction interaction. Neboglamine is an NMDA glycine-site PAM (positive allosteric modulator) — it enhances NMDA signaling. Memantine blocks NMDA signaling. The combination is pharmacologically incoherent (each would partially cancel the other). Dylan's V6 wiki has neboglamine on the WATCH-LIST anyway; this is a stack-safety reason in addition.

• High-dose CNS depressants (benzodiazepines, GHB, barbiturates): Additive sedation / cognitive blunting. Not a Dylan concern.

• Drugs that alkalinize urine (sodium bicarbonate, carbonic anhydrase inhibitors, certain renal-loss conditions): Reduce memantine clearance — accumulation possible. Athletes using sodium bicarbonate for ergogenic purposes (>0.3 g/kg loading doses) should know.

Neutral / safe co-administration

V4 stack: DHA (Carlson Super DHA Gems), Magtein (synergistic), Cognizin citicoline, NAC (synergistic), phosphatidylserine, Mg glycinate (synergistic), curcumin phytosome, rhodiola, theanine (mild synergy), tryptophan or glycine, D3+K2, beta-alanine, vitamin C, creatine.

V5 trajectory: modafinil (synergistic angle), bromantane (no documented interaction; pharmacologically distinct — bromantane is dopaminergic via tyrosine hydroxylase pathway, not NMDA), Adamax / Semax / Selank (no interactions documented; all are peptides cleared differently), ALCAR (neutral), apigenin (neutral), taurine (mild synergy via inhibitory neurotransmission), astaxanthin (neutral), L-tryptophan (neutral), cerebrolysin (synergistic in TBI use case), selegiline 1-2.5 mg (neutral; selegiline at low doses is MAO-B selective, no serotonergic interaction concern with memantine which is non-serotonergic), bupropion (neutral; bupropion is NDRI, no NMDA action — no interaction), propranolol PRN (neutral).

• CYP enzymes: Memantine bypasses CYP metabolism almost entirely. Not a substrate for CYP1A2, 2A6, 2C9, 2C19, 2D6, 2E1, 3A4. Memantine weakly inhibits CYP2B6 and CYP2D6 in human liver microsomes (in vitro), but at clinical concentrations the inhibition is judged not clinically relevant. Practical implication: memantine has the cleanest CYP profile of any centrally-acting drug Dylan might consider — no induction/inhibition concerns with modafinil (CYP3A4 inducer), enclomiphene (CYP2D6 substrate), bupropion (CYP2D6 inhibitor + 2B6 substrate), or selegiline.

• Renal handling drug interactions: Hydrochlorothiazide can reduce memantine clearance modestly. Cimetidine, ranitidine, quinidine, nicotine compete for OCT2/MATE1 — small kinetic effect, not clinically significant. Sodium bicarbonate at high doses can alkalinize urine enough to cut memantine clearance ~80% (theoretical accumulation risk).

• Dopaminergic drugs (L-DOPA, bromocriptine, pramipexole, etc.): Memantine has weak D2-high agonism and may modestly enhance dopaminergic effects. Used adjunctively in Parkinson's L-DOPA-induced dyskinesia. Not a contraindication.

• MAOIs (selegiline, rasagiline, tranylcypromine): No documented interaction. Memantine is not serotonergic and not significantly metabolized by MAO. Selegiline at 1-2.5 mg in Dylan's optional V5 list is MAO-B-selective and has no theoretical interaction with memantine.

• SSRIs (escitalopram, sertraline, etc.): No serotonin-syndrome mechanism (memantine is not serotonergic; no SERT inhibition; no MAO inhibition). The OCD-augmentation evidence demonstrates real-world combination safety with fluvoxamine, sertraline, escitalopram across multiple RCTs. Clinically used together routinely.

• Stimulants (methylphenidate, amphetamines): Combination established in ADHD-adjunct studies (Biederman 2014). No CYP interactions, no cardiac interactions documented at standard doses.

• Modafinil: No documented interactions. Different metabolic pathways, different mechanisms. Stack-safe.

• Anti-coagulants (warfarin): Possible mild effect on INR — case reports of INR fluctuation. Monitor if combined.

• Contraceptives: No documented interaction. Memantine doesn't affect estrogen/progestin metabolism.

• Alcohol: Pharmacodynamic interaction — both are CNS depressants in different ways. Acute alcohol potentiates memantine cognitive blunting; chronic alcohol may reduce memantine efficacy in tolerance-prevention use. Dylan is zero-alcohol baseline so non-issue.

Minimal actionable data — this is one of the more pharmacogenomically-quiet drugs.

• NR1I2 rs1523130 (PXR — pregnane X receptor) is the only genetic covariate identified in clinical pharmacokinetic studies (Sotaniemi-Cabrera et al., reviewed in PMC9145014). CT/TT carriers show slower memantine elimination than CC carriers. Effect size is modest. Not currently genotyped on 23andMe.

• OCT2 (SLC22A2) polymorphisms (rs316019 A270S being the most studied) affect renal handling of OCT2 substrates including metformin, cimetidine, and theoretically memantine. The clinical relevance for memantine specifically has not been demonstrated. May be visible in 23andMe raw data depending on chip version.

• MATE1 (SLC47A1) and MATE2-K (SLC47A2) polymorphisms — likely minor impact on memantine renal clearance; clinically unstudied.

• GRIN2A / GRIN2B (NMDA receptor subunit) polymorphisms — theoretically relevant to individual sensitivity to NMDA antagonism; clinically uncharacterized for memantine response.

• CYP polymorphisms (2D6, 2C19, etc.) — irrelevant. Memantine is not CYP-metabolized.

For Dylan (23andMe results pending June 2026): No actionable pharmacogenomic flags. If raw data shows OCT2 A270S variants, slightly slower renal clearance is plausible — start at 5 mg/day and don't titrate above 10 mg/day without renal function check. Otherwise, dose normally.

Cost reality check: $7-15/month with a GoodRx coupon. Among the cheapest centrally-active drugs Dylan could ever consider. For a deployed-as-needed compound, even a 3-month trial is <$50 total.

Recommendation for Dylan: Hold for trigger event (modafinil tolerance, classical-stim transition, TBI, treatment-resistant anxiety). When triggered, telehealth prescription via Sesame Care or similar ($30-50 visit), generic via GoodRx at local pharmacy ($8-15/mo). Standard tablet form (5 mg or 10 mg) is fine — no need for ER given the long native half-life.

• Baseline (before starting): Creatinine + eGFR (renal function — required to dose-adjust). Urine pH (rare relevance, but useful if athlete on bicarbonate). BP and HR resting. Cognitive baseline (PVT for vigilance, n-back for working memory, simple reaction time) — establishes a benchmark to detect any cognitive blunting at higher doses. Y-BOCS if OCD-trial. BRIEF-A if ADHD-adjunct. MMSE/MoCA only relevant in cognitive-decline target populations.

• During use: Renal function annually if used >12 months. Cognitive VAS weekly during titration (subjective check for blunting). BP monthly during titration if hypertension-prone. Subjective tracking: anxiety scale, sleep diary, perceived stim-tolerance freshness if using as tolerance modulation.

• Post-cycle (if discontinuing): Re-baseline cognition at week 2 post-stop (after 2 half-life washout). No formal post-cycle protocol needed — memantine is designed for chronic use, not cycled use.